Further development of Twinlay porous asphalt surfaces

Abstract

Road traffic noise (with tyre/road interaction being the predominating factor to the generation of noise production especially at vehicle speed above 50 km/h) is becoming an escalating problem that poses a threat to the environment. Ways and means of eradicating or at least retarding this problem have led to the development of Porous Asphalt surfaces which has excellent functionality. Porous asphalt has been used mainly for reducing aquaplaning subsequently reducing splash and spray thereby reducing accident rate during wet weather conditions, reducing road traffic noise and improves wet weather skid resistance Two layered construction so called "Twinlay" is a new development which was initiated in the Netherland with an intention of optimizing reduction to road traffic noise and also to solve the shortfalls (e.g. clogging) associated with the conventional single layer of porous asphalt. Twinlay is made up of a bottom layer of porous asphalt with a coarse single grained aggregate (11/16) and a thin top layer of fine porous asphalt (4/8). Twinlay has many advantages as opposed to the previous practises (single layer of porous asphalt) in South Africa, e.g the fine top layer acts as a sieve preventing sand or dirt from clogging the coarse bottom layer, and also, the fine surface texture of the top layer reduces tyre/road noise and many more. More research into road/traffic noise reveals that the acoustic properties of a conventional Twinlay porous asphalt surface can be further improved by introducing a thick double layer system (e.g. Superfine Twinlay) with a superfine top singlegrained aggregate mixture.